Tidy flags idref as an unknown attribute

FYI,
 
The latest (August) version of Tidy is flagging idref as an "unknown
attribute" in <label>.
 
<label idref="name">Name:</label>
<input type="text" id="name" />

Rick Roth 
Web Developer 
Rivio, Inc. 
rickr@rivio.com <outbind://21/rickr@rivio.com>